Veteran homelessness is a national crisis and Los Angeles has the highest homeless Veteran population in the US. Despite impressive progress in providing housing for Veterans, particularly through the HUD-VASH program, a fundamental problem remains: Permanent housing is a necessary first step, but not a sufficient condition, for successful community reintegration. Community reintegration, defined as full engagement in work, social, independent living, and recreational activities, does not arise automatically once housing is provided. Despite the provision of housing, recidivism (return to homelessness) is high. Further, the few relevant studies of non-VA samples demonstrate a failure to thrive after supported housing is provided (e.g., vocational and social functioning remain poor). HUD-VASH clinicians describe similarly poor outcomes in Veterans, but there are hardly any data on the types, severity, and causes of problems in community reintegration in recently-housed Veterans (RHVs). This information is essential for developing recovery- focused treatments that can be implemented in this complex, rapidly growing Veteran population. In 2015, our team established the VA Research Enhancement Award Program (REAP) on Enhancing Community Integration for Homeless Veterans in Los Angeles. The REAP is devoted to understanding the scope of reintegration problems, identifying their determinants, and developing novel interventions. We have identified two major challenges in our work with RHVs and their treatment providers. 1. Inadequacy of measures: Existing measures of community integration lack the sensitivity needed to identify the specific challenges faced by RHVs, and there have been no fine-grained assessments of how RHVs actually spend their time. 2. Poor rates of participation: It is extremely difficult to engage RHVs in treatment and research that require repeated visits to the VA campus. Consequently, our research assessments provide only single cross-sectional snapshots of integration that fail to capture the dynamic fluctuations in their lives. Furthermore, failure to engage in available treatment services contributes to recidivism and poor outcomes. We therefore believe it is necessary to look beyond traditional assessment and treatment modalities to address these challenges. New mobile technologies appear ideally suited this purpose. The goal of this proposal is to evaluate the feasibility of Digital Phenotyping (DP) delivered via mobile smartphone technology to assess community integration in RHVs with Serious Mental Illnesses (SMIs). We will use both active (Ecological Momentary Assessment [EMA] of social contact) and passive (Global Positioning System measures of mobility in the community) DP indices. Active EMA indices involve cueing participants to complete brief surveys multiple times per day over a week to obtain more fine-grained, ecologically valid information than traditional cross-sectional measures. Passive indices are automatically collected in the background using standard phone sensors. DP indices have never been examined in this population. To evaluate feasibility in this challenging population, we propose a 2-year mixed quantitative/ qualitative methods study with two phases. Phase 1 (Aim 1, Months 1-3) consists of focus groups with key stakeholders to adapt an existing EMA community integration survey (originally developed for SMI) for use in RHVs and to understand RHVs' views about passive data collection via smartphone. Phase 2 (Aim 2, Months 4-24) includes 27 RHVs with SMIs in HUD-VASH who will complete (a) baseline clinical assessments of community integration, (b) a 7-day (5 surveys/day) DP period to evaluate feasibility, (c) post-DP quantitative/ qualitative evaluations of acceptability. The proposal aims to break new ground in the use of mobile technologies, which have the potential for innovative assessment and treatment delivery applications for RHVs.